Multi-pass and Non-concentric Target Circular Synthetic Aperture Sonar
SERDP 2016 Project of the Year Award for Munitions Response
Circular Synthetic Aperture Sonar (CSAS) is a promising technique to classify and identify underwater objects, such as submerged or buried unexploded ordnance. It is easy to imagine CSAS being used to develop local training data to support acoustic surveys of the more than 400 Formerly Used Defense Sites that are potentially contaminated with submerged unexploded munitions. In the case of particularly high-value targets this technique may even be used for the survey. Under this year's winning project, Dr. Jermaine Kennedy (NSWC-PCD) and Dr. Timothy Marston (APL-UW) developed very sophisticated sonar processing algorithms to produce acoustic images and thereby advance the usability of CSAS.
During December 2014 and June 2015, Dr. Marston and Dr. Kennedy obtained sonar data of sample munitions and other objects in a variety of environments, ranging from flat and sandy seabed to areas comprised primarily of rock, coral, and complex limestone formations. The data were collected from an Autonomous Underwater Vehicle (AUV) instrumented with a dual-band sonar having a high frequency band in the hundreds of kilohertz and a low frequency band in the tens of kilohertz. The sonar heads travelled along circular paths at different heights around each object. The researchers wrote software to estimate the 3D position of the sonar head using the sonar data itself, and developed new algorithms for coherently combining the data from the multi-pass scans to reconstruct 3D images of targets and measure their 3D acoustic frequency responses.
Significant challenges included compensating for spatial and temporal sound propagation speed variations, the complexity of the local seafloor, and the 3D positioning uncertainties inherent to underwater navigation that complicate multiple pass synthetic aperture processing.
The results were impressive. Using relatively low frequency underwater sound waves, their techniques allowed the video-quality figure seen below to be produced. This work will generate an acoustic training database, enabling eventual use by commercial UXO survey contractors.
For this important work, Drs. Kennedy and Marston and their project team received the 2016 SERDP Project-of-the-Year Award for Munitions Response for their project titled Multi-pass and Non-concentric Target Circular Synthetic Aperture Sonar.
- Dr. Jermaine L. Kennedy - NSWC PCD
- Dr. Timothy M. Marston - APL-UW
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